The present invention relates generally to a sheet-fed press, and more particularly to a front guide position adjusting device for performing a positional adjustment of a printing sheet transported from a paper supply unit before forwarding it to a printing unit.
In a sheet-fed press, a printing sheet is conveyed from a paper supply unit by means of a feeder board and is then accurately positioned in a predetermined position upon effecting a positional adjustment of the printing sheet in a paper transportation direction and a direction perpendicular thereto. The paper is then sent to a printing unit while increasing the speed of the paper equal to the peripheral speed of a transfer drum. A front guide device effects a positional adjustment of the printing sheet in the direction of transportation of the printing sheet, and a side guide device effects a positional adjustment of the paper in the direction perpendicular to the transportation direction. A swing gripper grips the paper and transfers it to the transfer drum. The front guide device further adjusts a paper feeding distance to the swing gripper, to thereby adjust an image forming position on the printing sheet.
Japanese Utility Model Laid-Open Publication No. 57-177737 and Japanese Patent Laid-Open Publication No. 61-19255 disclose such front guide position adjusting devices. According to the former, a front guide rod is supported by an eccentric bearing or spherical bearing, and according to the latter, the front guide rod is supported by an adjusting arm, so that a plurality of front guide elements mounted on the front guide rod are altogether adjustable by an equi-distance in the direction of the paper transportation.
However, the above-described prior arts are disadvantages in the following respects. One disadvantage is that when an oblique positional adjustment of the printing sheet is carried out, i.e. when only one side of the printing sheet is moved by moving only one end of the front guide rod to adjust an image forming position on a printing sheet, another end of the front guide rod is correspondingly moved. Referring to FIG. 5, the one dotted-chain line indicated by reference character a shows a front guide rod position before adjusting left side thereof b, and a line indicated by reference character d shows the front guide rod position where the leftmost side thereof b has been moved by a distance c from the state indicated by the character a. When the front guide rod position is so moved, a reference mark f on left marginal side of the printing sheet e is moved by a distance g and a reference mark h on right marginal side of the printing sheet e is correspondingly moved by a distance i.
Another disadvantage is that even if one end of the front rod is moved by a predetermined distance, an actual moving distance of the printing sheet varies depending upon difference in paper size in the widthwise direction. Referring again to FIG. 5, in the case of a printing sheet e' having a reduced size in the widthwise direction as compared with the printing sheet e, a reference mark j in the left marginal portion of the paper e' is moved by a distance k, which distance is not equal to the distance g as the paper e is moved by. Accordingly, when it is desired that only the leftmost end of the front guide rod be moved by a predetermined distance, an actual moving distance of the leftmost end of the rod is appropriately determined by a skilled operator according to his experience taking the widthwise dimension of the paper into consideration. Further, the rightmost upper side portion of the printing sheet has to be backwardly moved attendant to the forward movement of the leftmost upper side portion of the printing sheet. This adjustment has also been made by the operator from his experience. Thus, the operations are intricate and take a long time. Besides, an adjustment cannot be carried out with high accuracy. Such disadvantages also exist when a right side image on the printing sheet is adjusted, and when positions of images on left and right sides of the paper are adjusted for different dimensions.